The invention relates to a hand tool in the form of a pliers for expanding hollow bodies.
In the operation of such hand tools, which embody the principle of pliers and therefore are also called expanding pliers, the procedure is to rotate the movable hand lever against the hand lever affixed to the casing and projecting approximately radially, on a circular path by an angle of about 90 degrees, so that the jaws of the expansion head contract fully, and so that these jaws can be inserted into the hollow body to be expanded, which as a rule is a pipe end. In this case the movable hand lever drives the jaws radially approximately parallel to the axis of the expansion or spreading wedge and in line with the pipe.
Starting from this ergonomically disadvantageous and tiring position, both hand levers must be squeezed together to an angular position of virtually zero, with a corresponding expenditure of effort, in order to perform the expansion process. In the case of a step-by-step expansion, this procedure must be repeated several times. In the meantime the end of each hand lever is enveloped by the fingers of each hand, and bringing the lever ends to their parallel position must be done only so far, so as to avoid pinching the fingers.
In the widening or expansion of metal pipes, the operating force, beginning from virtually zero, increases progressively. In the widening of plastic pipes or thin-walled, plastic coated metal pipes, a higher force is required at the very beginning of the widening process, i.e., precisely at an ergonomically unfavorable point. Moreover, in the case of plastic pipes a greater widening must be performed, since most plastics have a tendency to shrink back. The expansion pliers, however, must be usable for all materials and combinations thereof and, by interchanging the expansion head with other standardized expansion heads, they must be usable for different pipe diameters as well.
EP 0 397 570 B1 and the corresponding DE,690 10980 T2 have disclosed an expansion tool for pipe ends of annealed copper, in which the movable hand lever is journaled, not in the casing, but directly in the end of the expansion wedge on a first pivot pin. This hand lever is joined to the casing by a link or swing arm which is joined to the hand lever by a second pivot pin and to the casing by a third pivot pin. According to the statement of the problem, the result is that forces parallel to its axis are exerted on the expansion wedge.
But this problem cannot be solved by the stated means, for even FIG. 2 shows that the link is at a steep angle to the axis of the head toward the end of the swinging movement, and that the hand lever stresses the expansion wedge at an angle to its axis due to the first pivot pin, and this precisely at the instant of the greatest need for effort. Reason: The axes of the pivot pins are at the corners of a triangle, so that parallelograms of force must be taken into account. This also applies to the starting position according to FIG. 1. It is especially disadvantageous in this case that the expansion wedge guided in the casing protrudes especially far out from the guide with respect to the first pivot pin, namely just at a point at which the guide is especially short, because the casing has at that point a cut-out for the link and the swing arm. Thus, not only are considerable flexural forces exerted on the relatively thin expansion wedge right at the beginning, but also the latter exerts considerable edge pressure against its guide. Edge pressuresxe2x80x94that is, line contactsxe2x80x94lead not only to considerable wear, but also to a greater need for effort because any lubricant film that may be present will break down under such conditions. Also, the flying three-point suspension, due to free play, does not provide for accurate guidance of the hand lever on a circular path. In the embodiment currently on the market, the casing and both hand levers consist of a light metal, so that the tool has a low weight. But this is not the only criterion for the evaluation of the known tool.
Also known are expanding pliers in which the movable hand lever is journaled directly in the casing and acts on the expansion wedge through a cam or a curve. Such tools are disclosed in EP 0 417 674 B1, but do not provide sufficient working stroke of the expansion wedge for the expansion of plastic pipes.
Relief in regard to the necessary stroke length of the expansion wedge is provided in this case by the so-called rack-and-pinion expanders, in which the inside end of the expansion wedge is in the form of a rack and is driven by a pinion sector which is on the end of the movable hand lever which is journaled on a shaft directly in the casing. It is possible to control the leverage ratio and the length of the stroke by choosing the diameter of the semicircle of the teeth in the sector. In this case, of course, tilting forces are exerted on the expansion wedge at the guide end, depending on the flank angle of the teeth, but these forces are absorbed inside of the guide or casing without edge pressure, and can be limited in their effect by an appropriate guidance diameter and lubrication.
Such a rack expander is disclosed by DE 28 07 988 B2. But in this case the pinion sector is on the side of the hand lever affixed to the casing, with the result that the expansion wedge has its greatest diameter at its free end and is tensionally stressed. Consequently the expansion wedge is arranged replaceably in an additional sleeve with external teeth and must be replaced when the expansion head is replaced. The standardized expansion heads on the market cannot be used for this purpose. Furthermore, due to the position of the pinion sector, either the length of the movable hand lever is shortened or, for a given length, the free end of the hand lever projects further away from the casing.
A rack expander of this general class is disclosed by DE 42 00 020 C1 and the corresponding E 0 619 153 B1, wherein the pinion sector is disposed on the opposite side of the fixed hand lever. Consequently, the movable hand lever must reach beyond the casing and the guide, thereby improving the leverage ratio. The casing, the two hand levers and the expansion wedge are forged from high-strength steel, resulting in a relatively heavy tool. The frictional mating of steel with steel between the expansion wedge and the casing and guide results, despite lubrication, in a considerable requirement of effort which, in addition to the total weight, not only quickly tires the operator but also greatly stresses the teeth and the hand levers. Therefore breakage of the movable hand lever in the area between the pinion sector and hand lever has already been encountered whenever the operator has utilized the largest usable expansion head to expand other than soft pipe materials, after neglecting maintenance by regular lubrication. What is involved is a tool used mainly at construction sites and for repair purposes, in which maintenance is often neglected and misuse can occur.
Attempts have already been made to reduce the weight by using a light metal to make the casing and the hand lever incorporated therein and by joining a pinion sector of steel to a movable hand lever of a light metal. This combination, however, has not had a long useful life. The term, xe2x80x9clight metal,xe2x80x9d as used herein, is to be understood to refer to aluminum as well as light metal alloys, especially high-strength aluminum alloys containing at least 60% aluminum by weight.
The invention, therefore, is addressed to the problem of providing a hand tool of the kind described above which, while serving the same purpose as the device according to DE 42 00 010 C1 and the corresponding EP 0 619 153 B1, requires significantly less effort in operation, has considerably less weight, and provides greater safety against overstressing the driving system and against the danger of breakage.
The solution of the stated problem is accomplished according to the invention in the hand tool named in the beginning by the features according to the present invention, which relates in part to hand tool for the expansion of hollow bodies having a casing with a first hand lever affixed to the casing and projecting laterally, with a second hand lever made of steel and which is joined pivotally with the casing on the side turned away from the first hand lever and which bears a pinion sector partially encompassing the shaft and is brought beyond the casing. The first hand lever and the second hand lever form a pliers. A through bore is arranged in the casing for the guidance of a rack consisting of steel, whose one end within the bore cooperates with the pinion such that an expansion wedge can be displaced by a closing movement of the two hand levers. The casing has means by which an expansion head with radially movable expander jaws can be placed coaxially onto the outwardly tapered end of the expansion wedge, wherein said casing with the bore and the first hand lever affixed to the casing comprise a material selected from the group consisting of plastics and light metals, wherein said casting and said rack together form a low-friction mating of light material with steel.
Thus the stated problem is solved to the full extent; in particular the device, while serving the same purpose as the device of DE 42 00 020 C1 and the corresponding EP 0 619 153 B1, requires decidedly less operating force on account of the frictional mating of steel with light metal, amounting to only about 12% of the former force. The saving of effort becomes especially apparent whenever an expansion is performed in stages or step-wise by replacing the expanding wedges in the pipe end, for example with wedges whose active surfaces are configured as cone sector surfaces or as stepped surfaces of decreasing diameters. Moreover a perceptibly lower weight of only about 50% of the former weight, and substantially less tiring of the operator due to the substantially reduced operating force, and greater safety against overstressing the drive system and against breakage. The efficiency amounts to more than 80%.
In comparison with the state of the art initially described, the following additional advantages are achieved: The expansion head is easily replaced. The expansion wedge is broadly supported on the side opposite the xe2x80x9cbitexe2x80x9d and is not flexurally stressed. No edge pressure is created at the end of the guide, no breakdown of the lubricant film occurs, and wear is reduced. The leverage ratio does not change. Expansion wedges of greater pitch with respect to the system""s axis can be used, so that a greater expansion of plastic pipes of larger diameter, greater wall thickness and greater resistance to deformation. Moving the movable hand lever over an arcuate path becomes clearly better without exaggerated precision of the bearing, and also only one axis or pivot pin is needed. Standardized expansion wedges currently on the market can be used, with the insertion of an adapter in some cases.
In regard to the immense saving of the operator""s effort and the effects on the drive system of the device, one must bear in mind the following synergistic effect: Due to the low operating effort, the internal surface stresses and friction forces are also reduced, so that the operating effort is reduced, and so on. This advantage promotes the use of the tool in all possible positions, overhead, with arms outstretched, etc.
Instead of light metal or a light metal alloy, an impact-resistant plastic can be used for the casing and the hand lever affixed to it, reinforced in some cases with embedded fibers, which is likewise a xe2x80x9clight materialxe2x80x9d and has the same advantage of greatly reduced friction between the expansion wedge and the casing.
The term, xe2x80x9cLeichtmetallexe2x80x9d [light metals] is defined, for example, in xe2x80x9cRxc3x96MPP CHEMIE LEXIKON,xe2x80x9d 9th ed., 1996, Vol. H-L, on page 2479. Aluminum, magnesium and titanium are cited as important industrially; also, alloys of light metals are considered to be xe2x80x9cLeichtmetalle.xe2x80x9d
In the course of additional embodiments of the subject of the invention it is especially advantageous ifxe2x80x94either individually or in combination:
The second hand lever, consisting with the pinion sector of steel, has two flanges between which at least one opening, hole or recess is situated on at least a part of its length,
the second hand lever has at least three openings between which there are at least two bridges running lengthwise,
the second hand lever has between the pinion sector and the portion containing the openings a wedge-shaped intermediate section at whose tapered extremity the pierced section is formed,
the width of the flange is less than the width of the corresponding intermediate section,
the width of the at least one bridge is again less than the width of the flange,
the first hand lever, consisting with the casing of a light material, has two flanges between which at least one web exists along at least a portion of its length,
the first hand lever has between the case and the end of the lever a wedgeshaped intermediate piece extending from the casing, at whose tapered end the remainder of that portion is formed,
the width of the flange of the first hand lever is less than the width of the corresponding intermediate piece,
the width of the at least one bridge in the first hand lever is again less than the width of the flange,
the outer flanges of the hand levers are rounded in cross section on their outer sides and are provided at the ends of the hand levers with plastic sheaths whose outer sides are convergent, as seen from the system axis, when the levers are closed,
the hand levers are curved toward one another saber-wise,
the outsides of the intermediate pieces are convexly curved up to the edges which are at right angles to the system axis and cross at least substantially flush with the insides of the hand levers,
the casing is of oval shape in cross section through the system axis,
the expansion cone on the rack is made replaceable,
between the casing and the expansion head a replaceable adapter is provided, which has an internal bore into which the upper end of the expansion wedge can be retracted under the guidance of the internal bore, and/or, if
an adjusting screw is disposed in the casing, whereby the working angle of the movable second hand lever can be adjusted with respect to the casing, the radial expansion of the expander jaws can thus be controlled.